A total of 53,992 people were stopped at all British ports and airports in 2012-13. Photograph: Rex Features

Fresh concerns that Asian people are more than 11 times more likely than white people to be stopped at British airports and ports and questioned under counter-terrorism powers have been raised by the Equality and Human Rights Commission (EHRC).

A new experimental pattern of analysis of the ethnicity of the 50,000 people a year who are stopped to determine if they are involved in terrorism suggests that stereotyping rather than intelligence may be a key factor in the use of the powers under schedule 7 of the Terrorism Act 2000.

The powers, which were used in August to stop and seize documents from David Miranda, the partner of the former Guardian journalist Glenn Greenwald, require no prior suspicion and can only be lawfully used to determine whether an individual is "concerned in the commission, preparation or instigation of acts of terrorism".

Examinations under the powers can include basic questioning, a search and seizure of property and detention for up to nine hours.

The EHRC experimental analysis shows that there were high levels of examinations of passengers of certain ethnic backgrounds compared with white passengers.

The figures show that among the 53,992 people stopped at all British ports and airports in 2012-13, those who were Asian were 11.3 times more likely to be stopped than those who were white. Those who were black were 6.3 times more likely to be stopped and those who were mixed race were 3.6 times more likely to be stopped.

The EHRC briefing paper published on Thursday says that when a more detailed analysis was done of the 2010-11 schedule 7 stops on the basis of nine separate ethnic categories, including Indian, Pakistani, Bangladeshi and Chinese, those with a Pakistani background were shown to have a highly disproportionate number of stops.

Pakistani people were 52 times more likely to be stopped than white people, 135 times more likely to be questioned and examined for more than an hour, and 154 times more likely to be detained.

Mark Hammond, the EHRC chief executive, said schedule 7 was a necessary and useful power in the provision of national security.

He said: "If used intelligently and proportionately the police can protect the public against terrorist threats. However, stopping people based on stereotypes could lead to time and resources being misdirected and have a negative impact on relations with black and ethnic minority groups."

Hammond, who said the research suggested there might be an imbalance in the use of schedule 7 against ethnic minorities, added: "We are also concerned by the fact that people can be detained for lengthy periods without the reasonable suspicion required for other stop-and-search powers."

The equality commission says it will use the analysis to work with the Home Office and the police to ensure they are following their own guidelines, which ban discrimination on ethnic grounds in the exercise of these powers.

The code of practice for port Border Force officers and police special branch says they must ensure "that the selection of persons for examination is not solely based on their perceived ethnic background".

The analysis has been published as the House of Lords discusses changes to the schedule 7 powers as part of government amendments to the crime and antisocial behaviour bill.

The home secretary, Theresa May, is proposing to reduce the maximum period of detention from nine hours to six, to introduce new rights for the person detained to consult a solicitor and a ban on intimate searches, among other changes.

The government's official counter-terror watchdog, David Anderson QC, has also proposed that the power to detain people under schedule 7 without any suspicion of wrongdoing should be dropped completely. The commission has also backed amendments that would require "reasonable suspicion" to examine anybody for longer than one hour.